Numerical Simulation On Collapse Behavior Of RC Frames In The Case Of Fast Removing A Column

In recent years, accidental explosions and terrorist bombings have occurred in the industrial production and daily life frequently, which posed a grave threat to people's lives and property. Once the explosion occurred, It would cause not only direct damage to the people and property nearby but also the partial or total collapse of the building structure due to the blast loads lead to structural failure of key support member which thereby intensify the disaster. As for the study on progressive collapse of RC Frames under Blast Loads, due to its experimental particularity of high risk and cost, strict requirements of testing and the complexity of removing process, it is of great value in projects and theoretic developments to do research in the collapse-resistant capacity of and dynamic load effects on RC frames. In this paper, it will be explained from several respects as follows.(1) The finite element software AUTODYN is applied to respective numerical simulation analyses of close-in detonations and internal constraints detonation. It is found that the proposed method is efficient and reliable as compared to experiment results. This method is also applied to a mesh (cell size) convergence study to show that the ratio of the measured in terms of distance from the center of the charge and the charge radius has a great impact on the mesh convergence. According to the results, the converged solutions for cell size are achieved at r/308 (r/157.5) for F<4.5 and at r/81.9 (r/ 40.95) for r>11.7and can be determined in the range of r/308 (r/157.5) to r/81.9 (r/40.95) for 4.5<r<11.7.(2) Based on the experimental data of the explosion removing the support column of the RC Spatial Frame Structures, the three-dimensional finite element model was established by AUTODYN with the effect of gas-solid interaction considered. The numerical simulation methods in three-stage was applied to the case of the failure of the corner column or the side-and-mid column under blast loads showing that the failure modes of the column and the dynamic displacement of the beam-column joints simulation results were agreed well with the experiment which further verified the validity and reliablility of the proposed mehod.(3) For both cases above while ignoring the effect of floor slabs, the simulation results of AUTODYN demonstrated that the remaining structure can withstand greater ultimate load after the failure of the corner column, and the destruction of the side-and-mid column causes severer damage than that of the corner column.(4) The pushover analysis and instantaneously applied load method were utilized with the application of the software LS-DYNA in researching dynamic effect analysis during progressive collapse of a single-story RC plane frame. It indicates that the maximum value of the dynamic amplifying factor is less than 2 when the tructure moves in the elastic range and is more than 2 in elastoplastic stage with a positive correlation between the dynamic amplifying factor and the load and that there is a negative correlation between the dynamic amplifying factor and the load in plastic stage with the maximum value of the dynamic amplifying factor less than 2, comparied with a positive relationship and a maximum value of 2 in collapse limit stage until the dynamic divergence occurs.(5) The same method above was exercised in the dynamic effect analysis during prpgressive collapse of the multi-story RC plane frames. It shows that the risk of structural collapse of the frames caused by the failure of the side column is higer than that of the central column and that the end section of the frame beam connected to the damaged column is the control section of the frame during progressive collapse.(6) The same method above was also applied to the dynamic effect analysis during prpgressive collapse of the RC Spatial Frame Structures. According to tha results, the dynamic amplifying factor value of the column line increases with the addition of the load in the failure of the corner column while that of the adjacent column line decreases. However, during the failure of the side-and-mid column, the dynamic amplifying factor value of the column line grows with the load increasing and going beyond a certain value and has a positive relationship with that of the adjacent column line. The results also imply that destruction scale of the progressive collapse caused by the failure of the corner column is smaller than that of the side-and-mid column.